Dominant dimer emission provides colour stability for red thermally activated delayed fluorescence emitter

Cardeynaels, Tom, Etherington, Marc, Paredis, Simon, Batsanov, Andrei, Deckers, Jasper, Stavrou, Kleitos, Vanderzande, Dirk, Monkman, Andrew P., Champagne, Benoit and Maes, Wouter (2022) Dominant dimer emission provides colour stability for red thermally activated delayed fluorescence emitter. Journal of Materials Chemistry C, 10 (15). pp. 5840-5848. ISSN 2050-7526

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Official URL: https://doi.org/10.1039/D1TC04913E

Abstract

Colour purity and stability in multi-donor thermally activated delayed fluorescence (TADF) emitters has significant implications for commercial organic light-emitting diode (OLED) design. The formation of emissive dimer states in the well-known 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) chromophore at elevated dopant concentrations has recently been confirmed both experimentally and via theoretical calculations, indicating that multi-donor emitters such as 4CzIPN might suffer from a lack of colour stability due to the presence of multiple emissive states. This poses a serious issue for OLED manufacturers. In this work, dithieno[3,2-b:2′,3′-d]pyrrole (DTP) is applied as an alternative donor unit in a TADF emitter for the first time. In combination with isophthalonitrile (IPN), the 4CzIPN analogue termed 4DTPIPN is obtained. The strong electron donating nature of the DTP moiety gives rise to a red shift of the emission with respect to that of 4CzIPN. We identify that 4DTPIPN has a very stable emission spectrum throughout all solid-state thin film concentrations and host materials. Rather interestingly, this colour stability is obtained via the formation of dimer/aggregate species that are present even at 0.01 wt% concentration. Unfortunately, the higher colour stability is paired with a low photoluminescence quantum yield, making 4DTPIPN unviable for device applications. Nonetheless, this work shows the importance of dimer contributions, even at dilute doping concentrations. This molecule and study provide important understanding of the aggregation behaviour of small-molecule emitters necessary for the successful application of doped and, especially, non-doped OLED architectures.

Item Type: Article
Additional Information: Funding information: This work is supported by the University of Namur and Hasselt University PhD BILA scholarship T. Cardeynaels. The authors also thank the Research Foundation – Flanders (FWO Vlaanderen) for financial support project G087718N, G0D1521N, I006320N, GOH3816NAUHL and PhD scholarship S. Paredis. The calculations were performed on the computers of the {\textquoteleft}Consortium des {\'e}quipements de Calcul Intensif (C{\'E}CI){\textquoteright} (http://www.ceci hpc.be), including those of the {\textquoteleft}UNamur Technological Platform of High Performance Computing (PTCI){\textquoteright} (http://www.ptci.unamur.be), for which we gratefully acknowledge the financial support from the FNRS-FRFC, the Walloon Region and the University of Namur Conventions No. 2.5020.11, GEQ U.G006.15, U.G018.19, 1610468 and RW/GEQ2016. M.K. Etherington and A.P. Monkman are supported by EU Horizon 2020 Grant Agreement No. 732013 (HyperOLED). K. Stavrou and A.P. Monkman acknowledge the TADFlife project funded by the European Union{\textquoteright}s Horizon 2020-MCSA-ITN Research and Innovation Programme under grant agreement No 812872.
Subjects: F300 Physics
Department: Faculties > Engineering and Environment > Mathematics, Physics and Electrical Engineering
Depositing User: John Coen
Date Deposited: 02 Mar 2022 14:26
Last Modified: 19 Apr 2022 09:15
URI: http://nrl.northumbria.ac.uk/id/eprint/48595

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